Why not L6?
Engine length (almost) prohibits dual use in RWD + AWD/FWD.
Engine size always has 33% longer stroke (and proportionate connecting rod length) for same displacement and bore pitch.
Long stroke: tall deck = hood clearance problem (292 or Atlas in small car) + higher COG than V engine.
L6 block, crank, and head are weaker in torsion (bending) than V engine.

W/r/t "bottom end design"
4 main bearings with staged sizes is exactly the same as almost any other L6 engine in the same period. Name a 7 bearing L6 before 1960?

W/r/t "head design"
That's the one Mercedes 230 SL etc. used into the 1960s...